Tire inner tubes are ordinarily made from butyl rubber cross-linked or vulcanized to form a tube having good heat stability and physical properties. However, high temperatures and extreme conditions of use cause repeated expansion and contraction of the tire inner tubes. As a result, inner tubes made from these polymers have a limited useful life. For example, in many developing nations having bad roads and tropical and sub-tropical conditions, inner tubes are still used within tires. Inner tubes comprised of isobutylene based rubbers, such as butyl rubber, and chlorobutyl rubber, and EPDM rubber, do not have the proper properties to survive severe conditions of overloading and high temperatures. The inner tubes degrade, lose air, and become sticky, adhering to the tire. The inner tube cannot be removed from the tire, the tire cannot be retreaded, and thus the tire must be scrapped. These deficiencies in current inner tube compositions lead to excessive waste of tire composition and added cost of replacing a tire.
Most present day inner tube compositions lack the superior heat aging properties needed to produce a reliable, improved air impermeable tire inner tube capable of performing in severe service applications such as high speed, bumpy roads and overloading situations, which all may cause rapid deformation.
Inner tubes comprising butyl rubber are superior in barrier properties to inner tubes formed from any other rubber. However, certain applications require improved heat resistance which is normally obtained by blending Ethylene-Propylene (EP) or EPDM rubber with butyl in inner tube compounds. However, blending of EP or EPDM rubbers increases the air permeability of the rubbers.
U.S. Pat. No. 5,698,640 teaches isobutylene-co-brominated paramethylstyrene (EXXPRO™ ExxonMobil Chemical Company) bladders made from a low-bromine formulation. However, this low-bromine formulation does not possess proper cure properties needed for the production of inner tubes. The low bromine polymer will not develop the tensile and modulus strength needed for inner tubes. The cure system disclosed in U.S. Pat. No. 5,698,640 is considered to be too “scorchy” for inner tube processing.
U.S. Pat. No. 5,576,373 teaches the use of layered silicates in inner tubes while WO 9422680 includes a laundry list of rubbers that may be used for a variety of applications.
U.S. Pat. No. 5,650,454 discloses an elastomer composition comprising an isobutylene-paramethylstyrene copolymer rubber that may be used in inner tubes. The composition must contain an additive comprising a cross-linked fatty acid and a starch. The additive is said to increase tear resistance, but there is no suggestion that the compositions formed have enhanced thermal stability.
It has been known to use 1,6-hexamethylene-bis(sodium thiosulfate) (HTS, Flexsys Corp.) as a stabilizing agent, more specifically as a reversion inhibitor, in sulfur-vulcanized master batches of high diene rubber. See U.S. Pat. Nos. 4,417,012; 4,520,154; and 4,587,296 to Moniotte; and U.S. Pat. No. 5,508,354 to Talma et al. herein incorporated by reference for purposes of U.S. patent practice.
There is a need for an inner tube that will have enhanced thermal stability and physical properties under severe temperature and operating conditions.